1. Field of the Invention
The present invention relates to reticulated frame structures and, more particularly, to the use of nodal joints in the construction of such reticulated frame structures.
2. History of the Related Art
Generally, reticulated frame structures are made of a network of nodes and interconnecting members. The reticulated frame structure may have a single layer of interconnecting members, or there may be two or more layers connected parallel to one another and spaced apart by diagonal members. Such reticulated frame structures are commonly employed in the design, engineering, fabrication, and erection of, for example, domes, building facades, towers, stadium covers, bridges, and various other applications of space frames.
When the members are made of cylindrical tubes, connection to the nodes is generally pinned due to the configuration of the connection mechanisms. A typical pinned connection system employs a generally spherical node connected to a plurality of tubular framing members. Each tubular framing member is connected to the node by a connection assembly. The node typically has openings to receive parts of the connection assemblies, such as bolts. The ends of the tubular framing members are typically welded to other parts of the connection assemblies, such as end cones. The ends of the tubular framing members are often tapered to simplify or enhance the connection. Such a “tube and ball” system can be used to build extensive networks of nodes and framing members interlinked to form a variety of reticulated frame structures.
One existing type of tube and ball node system uses a spherical node with a plurality of rounded openings through which a bolt or pin is inserted and fixed therein. A funnel-shaped sleeve having a hollow cylindrical base is positioned between the spherical node and a hollow cylindrical framing member. A bolt is inserted through the framing member extending through the sleeve base and is rigidly attached by threading to the node. An externally accessible collar, which is rotationally fixed to the bolt, is provided to tighten the bolt to thereby attach the framing member to the spherical node. In this manner, shear, tensile, and compressive stresses are borne by the bolts.
In some cases, the compressive stresses are instead borne by the collar, as illustrated in U.S. Pat. No. 5,956,917 (Reynolds). The node system in this patent comprises a framing member, a block connector, an end cap, an end cap-block connector attachment means, and a collar. The end cap, movably attached to the block connector, is connected to both the collar and the framing member. To assemble the node system, the collar is slid onto the framing member and positioned at the end of the framing member. The framing member is then positioned relative to the block connector. Attached to the block connector is an end cap which is made to align with the framing member. A bolt is used to transfer the member tensile forces generated by the system. Once aligned, the end cap is shifted upwards and connected to the end of the framing member. The collar is then slid over the end cap toward the block connector and attached to the end cap. The collar transfers member compression forces generated by the system to the block connector.
A similar arrangement is described in U.S. Pat. No. 5,051,019 (Kohl). The node system in this patent comprises a faceted, spherical node member, and a conical connector member. The node member has a plurality of threaded sockets therein for receiving the conical connector member. The conical connector member has a nale screw-threaded portion extending axially from the narrow end of the connector member. The screw-threaded portion allows the conical connector member to be screwed into one of the thread sockets of the node member. A locating spigot extends axially from the larger end of the conical connector member. The locating spigot, in use, is fitted into the end of a tubular frame member. The tubular frame member has radially formed holes the rein for receiving pins, screws, and the like. The pins, screws, and the like extend through the holes in the tubular framing member and into a groove in the locating spigot. Such an arrangement holds the tubular framing member captive to the conical connector.
A characteristic of most existing node systems is that a bolt or similar attachment means is required to attach the framing members to the node. While the bolts are capable of transferring tensile forces to the node, they are generally less effective for transferring compressive forces and have very limited capacity to transfer bending moments. One reason for this drawback is the diameter of the bolts tends to be substantially smaller than the diameter of the framing members. As a result, for some of the existing systems, the compressive forces on the framing members are not transferred directly through the bolts. Instead, these forces are usually transferred through a collar, an end cap, a locknut, or the like. Such an arrangement increases the number of components required and adds complexity to the assembly process.
Further, existing systems have limited capacity to transfer moments at the joints. It has been shown that single layer systems with low capacity to transfer moments have extremely low buckling strength. This limitation has important implications in the case of glazing systems or glass structures. For example, the design of glass structural systems often requires the use of uncluttered systems with simple lines that provide unobstructed views and allow unobstructed light to come into the building. Single layer pinned connection systems have been employed for this purpose in small applications. However, because of the inherent lack of strength in single layer pinned connection arrangements, space frame systems with pinned connections are typically used in cluttered double layer configurations. Such double layer configurations are often undesirable because the excessive number of elements tends to prevent light from entering the architectural space.
In addition to forcing the use of double layer systems, for large or low curvature applications, pinned joint connections also adversely impact the design of the individual members. For example, when compared to the design a member with fixed connections, pinned joints at both ends require the use of shorter members or members with larger cross-sectional properties. The use of shorter members, in turn, increases the grid frequency and the number of components, and can result in increased manufacturing and field construction costs.
Furthermore, many of the existing system don't offer fully integrated glazing support elements. A secondary network of glazing support elements is typically added to provide support for the glass. This additional layer of members further clutters the glass support system. The fully integrated Spectraform glass support system eliminates the need of an additional layer of glass support elements.
Accordingly, it is desirable to provide a node system that does not use bolts or similar attachment means to attach the framing members to the node, or to transfer axial loads. It is further desirable to provide a simple node system that is capable of transferring out-of-plane moments, and wherein compressive forces may be transferred directly from the framing member to the connector. Finally, it is desirable to provide a system whose members incorporate fully integrated glass support system.